Public officials are just becoming aware of the nature and extent of the problem of contamination of the water supply from storage tanks leaking various chemicals into the soil. The latest EPA estimates in the United States place the volume of liquid hazardous waste stored at 20 billion gallons annually. These materials are stored at about 4,000 locations. It is also estimated that there are over 3/4 of a million individual motor fuel tanks and over 300,000 gas stations and trucking companies with gasoline storage tanks. As many as 1/3 of the petroleum tanks may be leaking. Over half are estimated to leak at a rate in an excess of 6 gallons per day. This roughly translates into 1.3 million gallons of fuel that is lost into the subsurface.
Soil excavation has been the traditional method for decontaminating a site with absorbed hydrocarbon contamination. It is often difficult to assess the full extent of the contamination. Besides being costly, excavating the soil merely changes the location of the contaminated soil. Hazardous sites are becoming fewer and fewer on expense and the regulation concerned with transporting the hazardous waste from the sites to the storage site makes this unattractive method of disposal. Current laws make the owner of the waste responsible forever for the stored waste whether it is the contaminated dirt or the spent carbon absorbent.
Soil ventilation is a cost effective way to decontaminate soil. This is effective in locations where the contamination has not reached groundwater. Currently there are two general methods used for remediation of groundwater before it can be discharged into a reinfiltration gallery, sewer or storm drain. These are carbon filtration or air stripping. Carbon filtration is not desirable on highly contaminated sites as the cost of carbon and its associated handling and disposal costs become prohibitive. With air stripping, the cost of carbon is eliminated leaving only replacement costs of packing as the major maintenance expense. However, in areas where emissions are controlled, carbon canisters for air polishing are required. When the soil is highly contaminated with hydrocarbon, the associated cost of carbon again becomes prohibitive.
One proposal for the elimination of gasoline vapors is to burn the recovered vapors. The level of hydrocarbons recovered in the vapor stream is usually not sufficient to maintain combustion by these vapors alone. Either additional fuel must be added to the vapor to sustain combustion or catalyst must be used to maintain combustion.